Fan Control

Howdy!

I need to control the speed of a 12 Volt DC fan as follows:

When the temperature is BELOW 270 degrees F, the fan speed is 100%.
When the temperature is ABOVE 320 degrees F, the fan speed is at the slowest possible rpm.
Between 270 and 320 degrees F, the fan speed varies in a linear fashion (or stepped percentages).

Despite countless hours of trying, I have NOT been successful.
Any assistance would be greatly appreciated!

Thanks,
JT

Post your current (or best) attempt.

How are the fan and the Arduino connected ?